The present invention relates to a rotary drum and a magnetic reproducing apparatus or a magnetic recording and reproducing apparatus using the rotary drum. In particular, the present invention relates to a technique enabling reproduction of signals from recording tracks of a type allowing higher recording density by multiple channels and narrower widths.
To achieve higher recording densities of magnetic recording media, it is effective to make track widths thereof narrower. As a method of reproducing signals from such a recording medium having narrow tracks, there is known a so-called non-tracking method. The non-tracking method is classified into a type of reproducing signals from recording tracks recorded by a so-called azimuth recording manner, and a type of reproducing signals from recording tracks recorded by a so-called non-azimuth recording manner.
FIG. 4 shows a positional relationship between reproducing heads of a related art rotary drum and recording tracks.
As shown in FIG. 4, according to the azimuth recording manner, recording tracks Tr+, Tr−, . . . can be formed on a magnetic recording medium “a” in such a manner as to be adjacent to each other. As a result, it is possible to realize two-channel magnetic recording mode and hence to further enhance the recording density.
The non-tracking method for reproducing signals from the recording track Tr+, Tr−, . . . recorded by the azimuth recording manner is carried by using a pair of reproducing heads R+1 and R+2 having the same azimuth angle and a pair of reproducing heads R−1 and R−2 having the same azimuth angle, each of which has a width wider than that of each recording track. According to this non-tracking method, even if the scanning loci of the reproducing heads R+1 and R+2 are fluctuated with respect to the +azimuth recording tracks Tr+, . . . either of the reproducing heads R+1 and R+2 is able to keep the on-track state as shown in FIG. 4 and hence to scan the recording track Tr+. At this time, the other one of the reproducing heads R+1 and R+2, which is on the off-track state, scans the −azimuth recording track Tr−; however, since the azimuth angle of the recording head is different from that of the recording track, there does not occur any crosstalk therebetween.
FIG. 5 is a schematic plan view of the related art rotary drum shown in FIG. 4.
As shown in FIG. 5, the +azimuth reproducing heads R+1 and R+2 and the −azimuth reproducing heads R−1 and R−2 are alternately arranged in the circumferential direction of a rotary drum “b” in such a manner as to be spaced from each other at equal intervals of 90°.
By the way, to enhance the density of magnetic recording, there has been a strong demand to make the recording track Tr narrower. For example, the track width Trw of the recording track Tr, which was generally of the order of 10 to 20 μm, has come to be made significantly narrow, and in recent years, the recording track Tr having the track width Trw of 1 to several μm has been put on practical use.
A rotary drum generally causes a “run-out” phenomenon (sometimes, called “fluctuation”), which leads to the fluctuation of the reproducing head R. The run-out includes RRO (Repeatable Run Out) and NRRO (Non Repeatable Run Out).
It is known that the RRO component is of the order of 2 to 4 μm as a critical value for a rotary drum using a ball bearing, and is of the order of 1 to 2 μm as a critical value for a rotary drum using a fluid bearing, and that the NRRO component is of the order of 0.2 to 0.4 μm.
For example, in the case of reproduction via a rotary drum using a ball bearing, the center value of scanning of a reproducing head of the rotary drum is fluctuated within a range of 2 μm because of the RRO component. This means that the locus of the reproducing head on a recording track Tr is fluctuated within a range of 2 μm with respect to the recording track Tr.
For a conventional type recording track Tr having a track width Trw=10 μm or more and a track pitch Trp=10 μm or more, even if the locus of a reproducing head is fluctuated within a fluctuation width of 2 μm, the reproducing head is able to scan the width, which is 8 μm at minimum, of the recording track Tr, and hence to sufficiently obtain reproduction signals.
The width of a recording track, however, has become narrower from the order of 10 to 20 μm to the order of 1 to several μm as described above, and the above-described non-tracking method fails to sufficiently obtain reproduction signals from such a very narrow recording track. For example, in the case of reproducing signals from a recording track Tr having a track width Trw=3 μm and a track pitch Trp=3 μm, if an RRO component of 2 μm occurs for a rotary drum, a reproducing head arranged on the rotary drum can scan only a width, which is 1 μm at minimum, of the recording track Tr, thereby failing to sufficiently obtain reproducing signals therefrom.